In a three-phase permanent magnet and induction-type motor, an application of a three-phase alternating current (AC) voltage to the stator windings induces a changing magnetic field around the rotor, with the force of an opposing magnetic field, whether induced or generated by a set of permanent magnets, causing a rotor shaft to rotate. Torque provided by the rotor shaft then can be harnessed and directed as needed for performing useful mechanical work within a system. For example, the rotor shaft can drive a belted alternator starter (BAS) system of a mild hybrid electric vehicle to enable rapid restart of the HEV after an Auto Stop event. Likewise, the rotor shaft can be selectively connected to a transmission shaft in a full hybrid design to electrically propel the vehicle.
To ensure proper functioning of the various components of a motor control circuit aboard the HEV, such as the electrical motor or motor/generator unit (MGU), an auxiliary power module (APM), and a power inverter module (PIM), a phase current sensor is ordinarily positioned within the MGU to directly measure each of the three phase currents transmitted to the MGU from the PIM. An electronic control unit or controller in communication with each of the three-phase current sensors can determine a phase current error by adding the various phase currents together and setting a diagnostic failure condition when the sum exceeds a zero value or a near-zero calibrated threshold. Such methods may be less than optimal for certain purposes, including the use of three different phase current sensors within the motor control circuit.